Heat build-up/fatigue measuring method for viscoelastic body and hydraulic servo flexometer

ABSTRACT

The major object of this invention is to provide a heat build-up/fatigue measuring method for a viscoelastic body and a hydraulic servo flexometer, that enable direct measurement of a strain (displacement) and a stress (load) applied to a test piece and realize highly precise measurement by controlling the stress and the strain applied to the test piece by hydraulic servo feedback control based on the measured strain and stress. 
     The hydraulic servo flexometer of this invention includes an upper anvil (22) and a lower anvil (18) having opposing parallel flat surfaces that form test piece holding surfaces, a hydraulic servo cylinder (19) having a piston rod (21) which is coupled to the upper anvil (22) or lower anvil (18) and which actuates in a direction perpendicular to the test piece holding surfaces, and a hydraulic servo mechanism for applying static and dynamic loads to the test piece (23).

TECHNICAL FIELD

The present invention relates to a heat build-up/fatigue measuringmethod for a viscoelastic body and a hydraulic servo flexometer, whichmeasure characteristics associated with heat build-up and fatigue byrepeatedly applying a load to a viscoelastic body, e.g., rubber.

BACKGROUND ART

Conventionally, as a test method of evaluating fatigue characteristicsassociated with heat build-up in a test piece, e.g., vulcanized rubber,by applying dynamic repeated loads to the test piece, ASTM No. D-623-67Method A is generally used. As a test machine for this purpose, aGoodrich Flexometer which complies with this standard has widely beenused.

FIG. 15 shows the schematic arrangement of the conventional Goodrichflexometer used in the above test, the operation of which will bedescribed hereinbelow. Referring to FIG. 15, a rotary motion of adriving shaft 203 driven by a driving motor 201 through a V-shapedpulley 202 is converted into a vertical motion by an eccentric 204provided to the driving shaft 203. A test piece 210 formed into theshape of a circular cylinder is sandwiched between an upper anvil 211and a lower anvil 212. A contact 214 of a thermocouple thermallyinsulated by an ebonite plate 213 is located at the central portion ofthe lower anvil 212, as shown in FIG. 16. Lead wires 215 extending fromthis contact 214 are connected to a temperature measurement device 216to record the temperature of the test piece 210.

Static and dynamic loads are applied to the test piece 210. Thecompression load of the static load is applied by a balance. Balanceweights 222 and 223 are respectively suspended from the two ends of alever arm 220 of the balance. A load weight 224 having an adjustableweight is placed on the rear balance weight 223. When the load weight224 is placed, the lever arm 220 tilts to push up the lower anvil 212which is fixed to the upper surface of the lever arm 220 through ananvil adjustment screw 218 such that its height can be adjusted in thevertical direction. Hence, the compression load is applied to the testpiece 210.

A differential transformer 225 is coupled to the rear portion of thelever arm 220. When the lever arm 220 tilts, the amount of itsdisplacement, i.e., the change amount of compression of the test piece210 is detected by the differential transformer 225. This detectionsignal is amplified by a motor control circuit (not shown) and convertedinto a rotation angle of a reversible motor 227. This rotation angle isdecelerated by a gear head 228 and converted into a rotation of arotating shaft, extending in the lever arm 220 in the longitudinaldirection, by a worm gear incorporated in the lever arm 220 through anelectromagnetic clutch 229. This rotating shaft rotates a helical gear.When the helical gear rotates, the anvil adjustment screw 218 rotates tomove the lower anvil 212 in the vertical direction. As a result, thelever arm 220 is always controlled to be horizontal.

After the static load is applied to the test piece 210 in this manner,the eccentric 204 is rotated by the driving motor 201 to move aconnecting rod 240 in the vertical direction, thereby moving in thevertical direction a connecting rod plate 242 coupled to the connectingrod 240 through a connecting rod pin 241. A cross bar holding upperanvil 244 is coupled to the connecting rod plate 242 through drivingrods 243. When the upper anvil 211 provided in the lower portionvertically moves upon rotation of the driving motor 201, a compressionstrain (dynamic load) is repeatedly applied to the test piece 210. Theamount of displacement of the upper anvil 211, i.e., the amount ofdeformation of the test piece 210 can be read by a deformation indicator246 through an indicator rod 245 extending upward from the cross bar244.

FIG. 17 shows the principle of the Goodrich flexometer described above.As is apparent from FIG. 15, the lever arm 220 can swing at its centerand is supported by a knife edge fulcrum 221. The balance weights 222and 223 each weighing 24 kg are respectively suspended from the two endportions of the lever arm 220 in order to give inertia to the lever arm220. Furthermore, the load weight 224 is placed on the left balanceweight 223 to apply a static load to the test piece 210 from the loweranvil 212 by a lever operation.

When the test piece 210 is strained by the static load to tilt the leverarm 220 to the left, a test piece support 231 connecting the lower anvil212 and lever arm 220 is lifted upward by a micrometer screw mechanism230 through rotation of the screw 218 to restore the horizontal state ofthe lever arm 220. The upper anvil 211 applies a dynamic load, thestrain of which has a constant amplitude, to the test piece 210 with aneccentric mechanism. This dynamic load is received by the inertia of thelever arm 220 through the lower anvil 212.

When the fatigue characteristics are to be evaluated based on the abovetest machine and test method, two types of tests (1) and (2) describedbelow are generally conducted.

(1) A static initial load is applied to the test piece underpredetermined temperature conditions. Furthermore, a sinusoidalvibration having a constant amplitude is applied to the test piece. Thetemperature of heat build-up and the creep amount of the test piece thatchange over time are measured.

(2) A static initial load is applied to the test piece underpredetermined temperature conditions. Furthermore, a sinusoidalvibration having a constant amplitude is applied to the test piece topromote fatigue. The temperature and time at which blow out occurs inthe central portion of the test piece are measured.

When a viscoelastic body causes dynamic fatigue, a physical changeoccurs in the viscoelastic body. This physical change together with heatbuild-up makes the interior of the viscoelastic body tacky. Volatilesubstances in the ingredients and the decomposed substance of theviscoelastic body gasify and accumulate in the viscoelastic body. Then,the interior of the viscoelastic body becomes porous so that the gaseoussubstances finally make a cavity inside the testpiece. This phenomenonis called blow-out.

In particular, in test (2), when measuring the temperature at whichblow-out occurs, the test is conducted while applying a vibration to thetest piece. The test is stopped when the temperature of heat build-up inthe test piece reaches an anticipated value. Then, the test piece is cutinto halves, and the blow-out, i.e., the porous state is observed by thehuman eye. At this time, if blow-out has not occurred, a test isconducted again under the same conditions by using a next test piece.The test is conducted with a higher temperature of heat build-up thanthe first test. The test piece is divided and observed. Alternatively,if a large number of pores formed by blow-out are observed, the test isconducted by lowering the temperature of heat build-up inversely. Testsare repeated in this manner until the temperature at which blow-outoccurs is determined. Accordingly, numerous tests become necessary.

However, the conventional Goodrich flexometer described above depends ona purely mechanical mechanism that applies a static load (load) to thetest piece with a lever arm by the principle of a lever, therebyapplying a dynamic deformation to the test piece with an eccentricmechanism. For this reason, the knife edge fulcrum that supports theentire inertia acting on the lever arm and the micrometer screwmechanism that requires high precision as it receives all the static anddynamic loads applied to the test piece tend to wear or be damaged.Then, the operating efficiency of the test machine is degraded or a highmaintenance cost is required.

The conventional Goodrich flexometer supports the test piece from belowwith the inertia of the lever arm. If, however, the lever arm is tiltedby the static strain of the test piece to delay anvil adjustment withthe micrometer screw mechanism, a tilted load is applied to the testpiece, disabling accurate measurement.

The conventional Goodrich flexometer measures the static deformationcomponent by mechanical inertia. However, whether the dynamic componentis completely removed is doubtful.

The conventional Goodrich flexometer cannot measure dynamic and staticstresses (loads) actually applied to the test piece, and regardingdeformation of the test piece, it can measure only the average of thedynamic components. Thus, only a macroscopic superficial result can beobtained.

In the conventional heat build-up/fatigue measuring method, since aflexometer which is a mechanical inertial system is employed,measurement can be performed only under the limited conditions that thestatic load is constant and the dynamic strain has a constant amplitude;a test can only be conducted under conditions that are far differentfrom actual conditions for use. Furthermore, information that areobtained by measurement are temperature rises of the test piece surfacecaused by internal heat build-up and deformation of the test piececaused by fatigue. However, in the test process,

(1) static and dynamic stresses cannot be measured, and

(2) regarding deformation, only the average of the dynamic componentscan be measured.

Therefore, only a macroscopic superficial result can be obtained, andbasic data necessary for clarifying the physical mechanism of blow-out,starting with a temperature rise caused by internal heat build-up andreaching destruction, cannot be measured, which is a defect in terms ofprinciple.

In measurement of blow-out, since observation is performed by the humaneye by dividing the test piece, the same test must be repeatedlyperformed from the beginning until blow-out is confirmed by exchangingthe test piece. This requires time and labor, not providing a highmeasurement efficiency.

In the conventional Goodrich flexometer, supply, testing, and dischargeof the test piece must all be performed by the person in charge ofmeasurement. When data is to be obtained by using many test pieces, theperson in charge of measurement cannot leave the flexometer, which is avery large burden.

Since the temperature of heat build-up is measured on the surface of thetest piece, the accurate internal temperature is not clear. When adynamic load is applied, the entire flexometer vibrates to disableaccurate measurement, leading to a decrease in measurement precision.

The present invention has been made in view of the above problems, andhas as its object to provide a heat build-up/fatigue measuring methodfor a viscoelastic body and a hydraulic servo flexometer which, whenevaluating fatigue characteristics associated with internal heat buildupof a viscoelastic body, e.g., vulcanized rubber, by applying dynamicrepeated loads to the viscoelastic body, can conduct the test byapplying static and dynamic loads to the circular cylindrical test piecealways perpendicularly to its axial direction by using a hydraulic servomechanism.

It is another object of the present invention to provide a highlydurable hydraulic servo flexometer which can directly measure the strain(displacement) and stress (load) applied to a test piece, therebyenabling highly precise measurement and which has no portion that maywear or be damaged.

It is still another object of the present invention to provide ahydraulic servo flexometer which, for the purpose of measuring basicdata necessary for clarifying the physical mechanism, can conduct thetest under the following four conditions:

(1) Changes in static and dynamic components of a stress are measuredunder the test conditions that the static strain is constant and thedynamic strain has a constant amplitude.

(2) Changes in static component of a stress and in dynamic component ofa strain are measured under the test conditions that the static strainis constant and the dynamic stress has a constant amplitude.

(3) Changes in static component of a strain and in dynamic component ofa stress are measured under the test conditions that the static stressis constant and the dynamic strain has a constant amplitude.

(4) Changes in static and dynamic components of a strain are measuredunder the test conditions that the static stress is constant and thedynamic stress has a constant amplitude.

It is still another object of the present invention to provide a heatbuild-up/fatigue measuring method for a viscoelastic body, which can settest conditions that are close to actual conditions for use in order toevaluate the fatigue characteristics, can obtain many pieces ofinformation, and can predict blow-out from these information withoutdividing the test piece.

It is still another object of the present invention to provide ahydraulic servo flexometer in which transfer, supply, testing, anddischarge of the test piece are automated to decrease the burden on theperson in charge of measurement, thus improving the measurementefficiency, and in which measurement precision can also be improved.

DISCLOSURE OF THE INVENTION

The first aspect of the invention is characterized, in a heatbuild-up/fatigue measuring method for a viscoelastic body which measuresheat build-up and/or fatigue of a viscoelastic body, in that a strain ora stress applied to a test piece is detected, and a servo mechanismwhich applies static and dynamic loads to the test piece is controlledbased on the detected strain or stress. In this invention, since thestatic and dynamic loads are applied to the test piece by using theservo mechanism, test conditions close to actual conditions for use canbe set, so that highly precise follow-up control and measurement can beperformed.

The second aspect of the invention is characterized, in a hydraulicservo flexometer for measuring heat build-up and/or fatigue of aviscoelastic test piece, by comprising an upper anvil and a lower anvilhaving opposing parallel flat surfaces that form test piece holdingsurfaces, a hydraulic servo cylinder having a piston rod which iscoupled to the upper anvil or the lower anvil and which moves in adirection perpendicular to the test piece holding surfaces, and ahydraulic servo mechanism for applying static and dynamic loads to thetest piece.

The third invention is characterized, in the hydraulic servo flexometerdescribed above, by comprising a strain detector for detecting a strainapplied to the test piece, and feedback hydraulic servo control meansfor controlling the hydraulic servo mechanism based on the detectedstrain.

The fourth invention is characterized, in the hydraulic servo flexometerdescribed above, by comprising a stress detector for detecting a stressapplied to the test piece, and feedback hydraulic servo control meansfor controlling the hydraulic servo mechanism based on the detectedstress.

In the second, third, and fourth aspects of the invention, the structureis simple and has no portion, e.g., a knife edge type fulcrum or amicrometer screw mechanism, that may be worn or damaged by the loadapplied during measurement. Thus, the measuring unit has highreliability and requires substantially no maintenance cost. Also, sincea feedback hydraulic servo system is constituted, highly precisefollow-up control and measurement can be performed.

The fifth aspect of the invention is characterized, in the hydraulicservo flexometer described above, by comprising a strain detector fordetecting a strain applied to the test piece, a stress detector fordetecting a stress applied to the test piece, a test condition selectorfor selecting a test condition or a combination of test conditions froma static component of the detected strain, a dynamic component of thedetected strain, a static component of the detected stress, and adynamic component of the detected stress, and feedback hydraulic servocontrol means for controlling the servo mechanism based on the selectedtest condition. In this invention, connection of a feedback loop can beselected by the test condition selector in accordance with fourcomponents, i.e., the static strain component, the dynamic straincomponent, the static stress component, and the dynamic stresscomponent. Also, measurement can be performed by selecting testconditions with an arbitrary combination. Consequently, data which isnecessary for clarifying fatigue characteristics associated withinternal heat build-up of, e.g., rubber, due to a large dynamicdeformation can be obtained within a region where such data cannot beobtained with the conventional Goodrich flexometer.

The sixth aspect of the invention is characterized, in a heatbuild-up/fatigue measuring method which measures heat build-up and/orfatigue of a viscoelastic body, in that a strain and a stress applied toa test piece are detected, static and dynamic loads applied to the testpiece are controlled by a hydraulic servo mechanism based on thedetected strain and stress, a creep amount, a complex modulus, and aloss tangent of the test piece are obtained based on the detected strainand stress, and a time point at which blow-out will occur is predictedbased on changes over time of the creep amount, the complex modulus, theloss tangent, and the temperature of heat build-up of the test piece.

The seventh aspect of the invention is characterized, in a heatbuild-up/fatigue measuring method which measures heat build-up and/orfatigue of a viscoelastic body, in that a strain and a stress applied toa test piece are detected, static and dynamic loads applied to the testpiece are controlled by a hydraulic servo mechanism based on thedetected strain and stress, a loss tangent of the test piece is obtainedbased on the detected strain and stress, and a relationship between aminimum value of loss tangent and a time point at which blow-out occursis obtained in advance, so that the time point at which blow-out occursis obtained from the minimum value of the loss tangent.

In the sixth and seventh aspects of the invention, since the static anddynamic loads are applied to the test piece by using the hydraulic servomechanism, the test conditions can be set as follows:

(1) the static strain is constant and the dynamic strain has a constantamplitude

(2) the static strain is constant and the dynamic stress has a constantamplitude

(3) the static stress is constant and the dynamic strain has a constantamplitude

(4) the static stress is constant and the dynamic stress has a constantamplitude

Accordingly, conditions that are close to the actual conditions for usecan be selected from these combinations. Since the creep amount, thecomplex modulus, and the loss tangent are obtained from the detectionvalues of the static and dynamic stresses and strains, basic data ofviscoelasticity can be measured. Accordingly, a time point at whichblow-out will occur is predicted from changes in these data. Since theinternal observation of the test piece need not be performed by dividingthe test piece, unlike in the conventional case, the number of times ofthe test can be decreased.

The eighth aspect of the invention is characterized, in a hydraulicservo flexometer for measuring heat build-up and/or fatigue of theviscoelastic body, by comprising an upper anvil and a lower anvilarranged in a thermostatic chamber to oppose each other to sandwich aviscoelastic test piece, a hydraulic servo mechanism for moving theupper anvil or the lower anvil in a vertical direction to apply staticand dynamic loads to the test piece, hydraulic servo control means forcontrolling the hydraulic servo mechanism based on a preset testcondition, a temperature detector for measuring a temperature of thetest piece, a strain detector for detecting a strain applied to the testpiece, and a stress detector for detecting a stress applied to the testpiece, and a transfer turret which is arranged between the upper anviland the lower anvil, has an insertion hole formed therein to receive atest piece inserted therein, is provided with fixing means for holdingand fixing the test piece inserted in the insertion hole, and rotatesintermittently, a rotary driving unit for rotating the transfer turret,opening means for opening the fixing means, thereby releasing the testpiece, and a control unit for controlling the hydraulic servo controlmeans, the rotary driving unit, and the opening means to fix the testpiece at a supply position with fixing means, rotating the transferturret until a test position and releasing the test piece, fixing thetest piece again with fixing means after the test, and rotating thetransfer turret until a discharge position and release the test piece.

The ninth aspect of the invention is characterized, in the hydraulicservo flexometer of the eighth aspect of the invention, by comprising asample supply cylinder arranged above the sample supply position of thetransfer turret in a vertical direction and having a sample stopper in alower side wall to be movable in a transverse direction, a verticallymovable sample platform arranged vertically below the sample supplycylinder, a stopper driving unit for moving the sample stopper in thetransverse direction, a platform driving unit for moving the sampleplatform in a vertical direction, and a control unit for controlling thestopper driving unit and the platform driving unit to load the sample onthe sample platform which has moved upward to a lower end of the samplesupply cylinder, and moving the sample platform downward such that thesample is located at a position of the fixing means of the transferturret.

The tenth aspect of the invention is characterized, in the hydraulicservo flexometer of the eighth aspect of the invention, by comprising asample discharge port provided vertically below the sample dischargeposition of the transfer turret, a sample discharge port shutterprovided at an inlet of the sample discharge port, a pusher movable in avertical direction vertically above the sample discharge port, a shutterdriving unit for moving the sample discharge port shutter, a pusherdriving unit for moving the pusher, and a control unit for controllingthe shutter driving unit and the pusher driving unit to open the shutterand to move the pusher downward only when discharging the test piece.

In the eighth, ninth, and tenth aspects of the invention, transfer,supply, testing, and discharge of the test piece are automated in thehydraulic servo flexometer by controlling the respective mechanisms withthe control unit, thereby improving the measuring efficiency.

The eleventh aspect of the invention is characterized, in a hydraulicservo flexometer for measuring heat build-up and/or fatigue of theviscoelastic body, by comprising an upper anvil and a lower anvilarranged in a thermostatic chamber to oppose each other to sandwich aviscoelastic test piece, a hydraulic servo mechanism for moving theupper anvil or the lower anvil in a vertical direction to apply staticand dynamic loads to the test piece, servo control means for controllingthe hydraulic servo mechanism based on a preset test condition, atemperature detector for measuring a temperature of the test piece, astrain detector for detecting a strain applied to the test piece, and astress detector for detecting a stress applied to the test piece, and inthat the temperature detector comprises a vertically movable temperaturesensor having a needle-like distal end, temperature sensor driving meansfor vertically moving the temperature sensor, and a control unit whichperforms a control operation in accordance with a detection value of thestrain detector so that the distal end of the temperature sensor islocated at a center of the test piece. In this invention, thedeformation amount of the test piece is obtained by the control unitfrom the detection value of the strain detector, the central position ofthe test piece in the direction of height is obtained, and thetemperature sensor is moved by the temperature sensor driving unit sothat the distal end of the temperature sensor always maintains itsposition. Since the distal end of the temperature sensor is located atthe central position of the test piece, accurate temperature measurementcan be performed.

The twelfth aspect of the invention is characterized, in a hydraulicservo flexometer for measuring heat build-up and/or fatigue of theviscoelastic body, by comprising an upper anvil and a lower anvilarranged in a thermostatic chamber to oppose each other to sandwich aviscoelastic test piece, a hydraulic servo mechanism for moving theupper anvil or the lower anvil in a vertical direction to apply staticand dynamic loads to the test piece, hydraulic servo control means forcontrolling the hydraulic servo mechanism based on a preset testcondition, a temperature detector for measuring a temperature of thetest piece, a strain detector for detecting a strain applied to the testpiece, and a stress detector for detecting a stress applied to the testpiece, and in that the hydraulic servo flexometer is accommodated andfixed in a hollow frame, and a vibration absorbing member is packed inthe frame. In this invention, the frame that supports the test portionof the flexometer is made hollow, and the vibration absorbing member ispacked in the hollow frame, so that any vibration of the test portionitself is prevented, thereby preventing an increase in measurementerror.

The thirteenth aspect of the invention is characterized, in a hydraulicservo flexometer for measuring heat build-up and/or fatigue of theviscoelastic body, by comprising an upper anvil and a lower anvilarranged in a thermostatic chamber to oppose each other to sandwich aviscoelastic test piece, a hydraulic servo mechanism for moving theupper anvil or the lower anvil in a vertical direction to apply staticand dynamic loads to the test piece, hydraulic servo control means forcontrolling the hydraulic servo mechanism based on a preset testcondition, a temperature detector for measuring a temperature of thetest piece, a strain detector for detecting a strain applied to the testpiece, and a stress detector for detecting a stress applied to the testpiece, and an air circulation plate arranged on a surface opposing airblowing means of the thermostatic chamber to circulate air along a sidewall. In this invention, since the air circulation plate is arranged inthe thermostatic chamber, the temperature distribution in thethermostatic chamber is uniformed. Thus, the temperatures of therespective test pieces are uniformed to decrease variations inmeasurement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially sectional side view showing the arrangement of ahydraulic servo flexometer body according to the first embodiment of thepresent invention;

FIG. 2 is a block diagram showing the control circuit of the hydraulicservo flexometer according to the present invention;

FIG. 3 is a schematic diagram showing a hydraulic servo flexometeraccording to the second embodiment of the present invention;

FIG. 4 is an explanatory diagram of measurement done by using thishydraulic servo flexometer;

FIG. 5 is an explanatory diagram of another measurement done by usingthis hydraulic servo flexometer;

FIG. 6 is a graph showing the sinusoidal waveforms of strain and stress;

FIG. 7 is a graph of measurement data indicating the relationship amongthe heat build-up temperature, the creep amount, and the loss tangent;

FIG. 8 is a diagram showing a hydraulic servo flexometer according tothe third embodiment of the present invention;

FIG. 9(a) and FIG. 9(b) are diagrams showing the transfer turret of theautomatic hydraulic servo flexometer shown in FIG. 8;

FIG. 10 is a flow chart for explaining the operation of the transferturret;

FIG. 11 is a diagram showing the sample supply mechanism of theautomatic hydraulic servo flexometer;

FIG. 12 is a diagram showing the test mechanism of the automatichydraulic servo flexometer;

FIGS. 13(a) to 13(c) are views for explaining the operation of atemperature sensor;

FIG. 14 is a diagram showing the sample discharge mechanism of theautomatic hydraulic servo flexometer;

FIG. 15 is a diagram showing a conventional Goodrich flexometer;

FIG. 16 is a diagram showing the temperature sensor portion of theconventional Goodrich flexometer; and

FIG. 17 is a schematic diagram showing the principle of the conventionalGoodrich flexometer.

BEST MODE FOR CARRYING OUT THE INVENTION

The preferred embodiments of the present invention will be described indetail with reference to the accompanying drawings.

First Embodiment

FIG. 1 is a partially sectional view showing the arrangement of ahydraulic servo flexometer body according to the first embodiment, whichemploys a heat build-up/fatigue measuring method for a viscoelastic bodyaccording to the present invention.

Referring to FIG. 1, reference numeral 11 denotes a base; 12, a supportcolumn; 13, an upper plate; 14, nuts; 15, a load cell support table; 16,a compression load cell; 17, a lower anvil connecting rod; 18, a loweranvil; 19, a hydraulic servo cylinder; 20, a fixing bolt for thehydraulic servo cylinder; 21, a piston rod; 22, an upper anvil; 23, atest piece; 24, a displacement detector; and 25, a thermostatic chamber,respectively.

The base 11 is horizontally installed on the floor surface of ameasurement room, and four support columns 12 extend vertically upwardfrom the four corners of the substantially square base 11. The upper endportion of each support column 12 forms a screw to which thesubstantially square upper plate 13 is horizontally attached with twonuts 14. The load cell support table 15 is placed on the upper surfaceof the base 11, and the compression load cell 16 for detecting a stressapplied to the test piece is placed on the load cell support table 15.The lower anvil 18 is fixed to the upper portion of the compression loadcell 16 through the lower anvil connecting rod 17 extending through thelower surface of the thermostatic chamber 25.

The hydraulic servo cylinder 19 depends from the upper plate 13. Thedisplacement detector 24 for detecting the displacement of the piston isprovided to extend upward from the hydraulic servo cylinder 19 throughthe upper plate 13. The piston rod 21 of the hydraulic servo cylinder 19extends through the upper surface of the thermostatic chamber 25 and isconnected to the upper anvil 22 in the thermostatic chamber 25. The testpiece 23 is sandwiched between the upper anvil 22 and the lower anvil18. The upper anvil 22, the test piece 23, and the lower anvil 18 areadjusted to a predetermined test temperature by the thermostatic chamber25.

FIG. 2 is a block diagram showing the arrangement of a feedback servocontrol system that controls the hydraulic servo flexometer bodydescribed above.

Referring to FIG. 2, reference numeral 24 denotes the displacementdetector; 16, the compression load cell; 26 and 27, amplifiers; 28 and29, AC/DC component separating circuits; 30, the AC component of adisplacement signal; 31, the DC component of the displacement signal;32, the AC component of a stress signal; 33, the DC component of thestress signal; 34, a test condition selector; 35, a dynamic componentcontrol signal; 36, a dynamic component measurement signal; 37, a staticcomponent control signal; 38, a static component measurement signal; 39and 40, subtracters; 41 and 42, potentiometers; 43, an adder; 44, aservo amplifier; 45, a hydraulic servo valve; and 46, ameasuring/recording unit, respectively.

Referring to FIG. 2, the displacement of a test piece (not shown) isconverted into an electric signal by the displacement detector 24, isamplified by the amplifier 26, and is separated into the AC component 30and DC component 31 of a displacement signal by the AC/DC componentseparating circuit 28. Similarly, the load (stress) of the test piece isconverted into an electric signal by the compression load cell 16, isamplified by the amplifier 27, and is separated into the AC component 32and DC component 33 of a load signal by the AC/DC component separatingcircuit 29.

The signals 30 to 33 detected and separated in the above manner areinput to the test condition selector 34. A combination of two testconditions are selected from static strain, dynamic strain, staticstress, and dynamic stress, and measurement/recording targets areselected from the remaining conditions.

More specifically, the following four conditions can be selected by thetest condition selector 34 to conduct the test.

(1) Changes in static and dynamic components of a stress are measuredunder the test conditions where the static strain is constant and thedynamic strain has a constant amplitude.

(2) Changes in static component of a stress and in dynamic component ofa strain are measured under the test conditions where the static strainis constant and the dynamic stress has a constant amplitude.

(3) Changes in static component of a strain and in dynamic component ofa stress are measured under the test conditions where the static stressis constant and the dynamic strain has a constant amplitude.

(4) Changes in static and dynamic components of a strain are measuredunder the test conditions where the static stress is constant and thedynamic stress has a constant amplitude.

The test conditions selected by the test condition selector 34 areextracted as the dynamic component control signal 35 and staticcomponent control signal 37, and are respectively input to thesubtracters 39 and 40 as minuends. Voltages corresponding to thepredetermined values of the test conditions set by the potentiometers 41and 42 are applied to the subtrahend inputs of the subtracters 39 and40, respectively. The subtraction results output from the subtracters 39and 40 are added to each other by the next adder 43 to form a servocontrol signal. This servo control signal is sent to the servo amplifier44. The servo amplifier 44 amplifies the servo control signal to drivethe hydraulic servo valve 45, thereby controlling the hydraulic pressuresupplied to the hydraulic servo cylinder 19. In this manner, the staticand dynamic loads complying with the test conditions are applied to thetest piece 23 from the piston rod 21 of the hydraulic servo cylinder 19through the upper anvil 22.

The measurement targets selected by the test condition selector 34 areextracted as the dynamic component measurement signal 36 and staticcomponent measurement signal 38, and are recorded by themeasuring/recording unit 46.

This embodiment has a simple structure and has no portion, e.g., a knifeedge fulcrum or micrometer screw mechanism, that may be worn or damagedby the load applied during measurement. Thus, the measurement unit has ahigh reliability and requires substantially no maintenance cost. Since afeedback servo system is constituted, highly precise follow-up controland measurement can be performed.

The feedback loop can be connected/switched by the test conditionselector among the four conditions, i.e., the static strain component,the dynamic strain component, the static stress component, and thedynamic stress component, and the measurement can be performed byselecting test conditions in arbitrary combinations. Therefore, datanecessary for clarifying the fatigue characteristics associated withinternal heat build-up of, e.g., rubber, occurring upon large dynamicdeformation can be obtained within a region where such data cannot beobtained with the conventional Goodrich flexometer.

Second Embodiment

FIG. 3 is a schematic diagram showing a hydraulic servo flexometeraccording to the second embodiment of the present invention. Thisembodiment provides a hydraulic servo flexometer which measures heatbuild-up/fatigue characteristics while measuring the temperature of thetest piece, thereby predicting a time point at which blow-out willoccur.

In the hydraulic servo flexometer of this embodiment, a disk-shapedupper anvil 52 and a disk-shaped lower anvil 53 that vertically sandwicha circular cylindrical test piece 51 are provided to oppose each other.The upper anvil 52 is directly coupled to a load cell 54 serving as astress detector provided above it, through a rod. The lower anvil 53 isdirectly coupled to a hydraulic servo cylinder 55 of a hydraulic servomechanism which is provided below it, through a rod. Furthermore, thehydraulic servo cylinder 55 is directly coupled to a differentialtransformer 56 serving as a strain detector. The upper anvil 52 andlower anvil 53 are accommodated in a thermostatic chamber 57. Thetemperatures of the upper anvil 52 and lower anvil 53 are held andcontrolled to a predetermined value by a heater 60 of a temperaturecontroller 59 while they are detected by a thermocouple 58. The centralportion of the upper anvil 52 including the load cell 54 forms a hollowportion, and a temperature sensor 61 having a needle-like distal end isinserted in this hollow portion. A temperature sensor inserting servomotor 62 is controlled such that the distal end of the temperaturesensor 61 is always located at the center of the test piece 51 in thedirection of height in accordance with the deformation of the test piece51 in the direction of height.

Values detected by the load cell 54, the differential transformer 56,and the temperature sensor 61 are input to a computer 67 through ananalog unit 65 and an interface 66, and the measurement results areoutput to a printer 68 or a plotter 69. The computer 67 is connected toa servo control circuit 70 through the interface 66 and the analog unit65 to control the hydraulic servo cylinder 55. The hydraulic servocylinder 55 is actuated and stopped by a hydraulic unit 71.

The operation of this hydraulic servo flexometer will be described. Thecircular cylindrical test piece 51 is arranged between the upper anvil52 and lower anvil 53 to be sandwiched between them, and the interior ofthe thermostatic chamber 57 is held at the measurement temperature. Theservo control circuit 70 controls the hydraulic servo cylinder 55 undertest conditions set by the computer 67, to apply predetermined staticand dynamic loads to the lower anvil 53. In this manner, thepredetermined static and dynamic loads are applied to the test piecethrough the lower anvil 53. At this time, the static and dynamic strainsof the test piece are detected by the differential transformer 56directly coupled to the hydraulic servo cylinder 55, and the static anddynamic stresses of the test piece are detected by the load cell 54directly coupled to the upper anvil 52. The temperature of the testpiece 51 is detected by the temperature sensor 61. These detectionvalues are input to the computer 67 through the analog unit 65 andinterface 66, as described above, to calculate the creep amount, thecomplex modulus, and the loss tangent. The calculated creep amount, thecomplex modulus, and the loss tangent are output to the printer 68 orthe plotter 69. Based on these detection values of the strains andstresses, the servo control circuit 70 controls the hydraulic servocylinder 55 to comply with the predetermined test conditions.

In the hydraulic servo flexometer of this embodiment, a hydraulic servomechanism is employed as the static and dynamic load means, and thefeedback servo control system is constituted by combining thedifferential transformer as the strain detector and the load cell as thestress detector, in the same manner as in the first embodiment. Thus,measurement in accordance with condition setting which varies very muchcan be performed with a very simple mechanism.

Since the hydraulic servo mechanism is employed, the followingmechanical advantages are obtained.

(1) The hydraulic servo flexometer has no portion that may wear or bedamaged upon application of an excessive load.

(2) The structure is simple.

(3) Control can be performed freely with reference to both displacementand stress.

(4) Since a feedback servo system can be constituted, highly precisefollow-up control and measurement can be performed.

Furthermore, measurement can be performed under the following fourconditions so that test conditions that are close to actual conditionsfor use can be set.

(1) Changes in static and dynamic components of a stress are measuredunder the test conditions where the static strain is constant and thedynamic strain has a constant amplitude.

(2) Changes in static component of a stress and in dynamic component ofa strain are measured under the test conditions where the static strainis constant and the dynamic stress has a constant amplitude.

(3) Changes in static component of a strain and in dynamic component ofa stress are measured under the test conditions where the static stressis constant and the dynamic strain has a constant amplitude.

(4) Changes in static and dynamic components of a strain are measuredunder the test conditions where the static stress is constant and thedynamic stress has a constant amplitude.

Among the above test methods, the measurement contents of items (3) and(4) will be described in detail.

Test method (3) will first be described. FIG. 4 is a diagram forexplaining measurement with test method (3). Although this is a testmethod that allows measurement even with the conventional Goodrichflexometer, how to apply the static stress and dynamic strain differslargely. While a constant initial load (stress) ΔFs applied to the testpiece 51 is always maintained by the hydraulic servo cylinder 55 basedon the detection value of the load cell 54, a constant sinusoidalamplitude (strain) ΔLd is applied to the test piece 51 based on thedetection value of the differential transformer 56, to promote fatigueof the test piece 51. When the test piece 51 generates heat, it promotesdynamic fatigue simultaneously, so that its internal stress decreasesand its sinusoidal stress ΔFd also decreases. Since the constant initialload ΔFs is always applied to the test piece 51 together with thesinusoidal stress ΔFd, an initial strain ΔLs increases. This initialstrain ΔLs is traced as the creep amount, and simultaneously thetemperature of heat build-up in the test piece 51 is also measured bythe temperature sensor 61.

FIG. 5 is a diagram for explaining measurement with test method (4).This test is enabled by a hydraulic servo flexometer. When a constantinitial load ΔFs (detected by the load cell 54) is applied to the testpiece 51, a static initial strain ΔLs (detected by the differentialtransformer 56) is generated in the test piece 51. During the test, ΔFsis always maintained at the constant value by the hydraulic servocylinder 55, and a sinusoidal amplitude (strain) ΔLd is applied to thetest piece 51 such that the sinusoidal stress ΔFd of the test piece 51becomes always constant. When the test piece 51 generates heat, itpromotes dynamic fatigue simultaneously, so that its internal stressdecreases. Since the sinusoidal amplitude is controlled so that aconstant stress is always applied, the amplitude (strain) ΔLd increasesas the internal stress decreases. Since the constant initial load ΔFs isalways applied to the test piece 51 together with the amplitude ΔLd, theinitial strain ΔLs increases. This initial strain ΔLs is traced as thecreep amount, and simultaneously the temperature of heat build-up by thetest piece 51 is also measured by the temperature sensor 61.

In any of the above four test conditions, static and dynamic stressesand strains are applied by the hydraulic servo cylinder, and the initialstrain (creep amount) ΔLs and the sinusoidal strain ΔLd are detected bythe differential transformer and the sinusoidal stress ΔFd is detectedby the load cell.

A loss tangent tanδ can be obtained from the sinusoidal strain ΔLd andsinusoidal stress ΔFd. FIG. 6 is a graph for explaining the waveforms ofthese strain and stress. If the test piece is a viscoelastic body, thewaveform of the sinusoidal strain ΔLd has a phase differencecorresponding to an angle δ from the waveform of the sinusoidal stressΔFd. The tangent of the phase angle δ is called the loss tangent tanδ,which represents the magnitude of the viscoelastic element. As thetangent δ increases, the viscosity increases; as it decreases, theviscosity decreases so that the viscoelastic body becomes close to anelastic body.

In this system, since the sinusoidal strain and stress applied to thetest piece are detected simultaneously, the dynamic viscoelasticity canbe calculated in accordance with the following equation.

When a sinusoidal strain ε having an amplitude ε₀ is applied to the testpiece, the sinusoidal strain is given by:

    ε=ε.sub.0 e.sup.iet                        (1)

where t: time, e: the base of natural logarithm, and ω: the angularfrequency.

At this time, the phase of the stress δ generated in the test pieceadvances by δ, as shown in FIG. 6. The stress at this time is a complexnumber consisting of a component in phase with the strain and acomponent having a phase lead of π/2 with respect to the strain.

An elastic modulus E is defined as the ratio of stress to strain, and isgiven in the form of a complex number in accordance with the followingequation (2):

    σ=E*•ε=(E'+iE")ε               (2)

where

i: an imaginary unit (i=√-1),

E': the dynamic storage modulus, and

E": the dynamic loss modulus

The loss tangent δ is given by:

ti tanδ=E"/E' (3)

In measurement of changes in dynamic viscoelasticity upon changes intemperature, when E', E", and tanδ are calculated as a function of thetemperature of heat build-up by the test piece while setting thefrequency at a constant value, transition, relaxation phenomena, and thelike can be determined from the variance of E' and absorption of E". Theblow-out temperature can be predicted and the fatigue mechanism can beanalyzed by analyzing the transition, the relaxation phenomena, and thelike.

FIG. 7 shows the characteristics curves of the fatigue test of a tirerubber obtained by measurement with test method (4). Test method (4) isselected because its conditions are close to the conditions for use ofthe tire. More specifically, in a vehicle tire, the initial load(stress) is the pneumatic pressure, the dynamic stress having a constantamplitude is the weight of the vehicle, and the frequency is the drivingspeed. In the case of an actual tire, a decrease in stress of thedynamic strain does not occur. Accordingly, test method (4) in which aconstant initial stress and a sinusoidal stress having a constantamplitude are applied to the test piece is appropriate as the testcondition.

The test of the test piece was started at an initial temperature of 100°C. After the start of the test, the temperature of heat build-up and thecreep amount increase sharply and the loss tangent tanδ decreasessharply, and then they stabilize slightly. When a point where blow-outoccurs is obtained by dividing the test piece and visually inspectingthe interior of the test piece, as in the conventional case, blow-outstarts to occur at a time point where the loss tangent has slightlyincreased from its minimum value. In the case of the test piece made ofsuch a material, it was found out that a predetermined relationship wasestablished between the minimum value of the loss tangent tanδ and thepoint where blow-out occurred. Therefore, if an equation defining thisrelationship is obtained in advance, the time point at which blow-outoccurs can be obtained from the minimum value of the loss tangent tanδ,and the temperature of heat build-up by the test piece and the creepamount of the test piece at this time can also be obtained.

Although the above case is merely an example, the fatiguecharacteristics of a viscoelastic body in actual use can be obtainedsince the measurement signals of both strain and stress can be obtainedas electric signals with a high resolution at a high speed under testconditions close to the actual conditions for use. In particular, sincethe creep amount, the complex modulus, and the loss tangent can beobtained from the detected values of the strain and stress, datanecessary for clarifying blow-out can be obtained, thus enablingprediction of blow-out. As compared to conventional detection ofblow-out by visual observation through division, the number of samplescan be decreased. Also, since the time point at which blow-out occurscan be obtained by calculation, variations according to the skill of theperson in charge of measurement can be prevented. Also, since a test canbe performed such that the dynamic stress amplitude becomes constant, ahard viscoelastic body that cannot be tested with the conventionalGoodrich flexometer can be tested.

Third Embodiment

FIG. 8 shows the entire arrangement of a hydraulic servo flexometeraccording to the third embodiment of the present invention. This systemis a hydraulic servo flexometer having an automatic measurementmechanism and its basic arrangement is identical to that of the systemshown in FIG. 3. Thus, the corresponding portions are denoted by thesame reference numerals, and a detailed description thereof will beomitted. The test unit shown in FIG. 3 is incorporated in a centralportion surrounded by a base 75 at the lower portion of the main body,two side frames 76, and an upper frame 77. The interiors of the two sideframes 76 are hollow and packed with sand 74 as the vibration absorbingmaterial. This aims at preventing vibration of the test unit itself thatincreases measurement errors.

Both upper and lower anvils 52 and 53 are located at the center of athermostatic chamber 57, and the systems for supplying, transferring,testing, and discharging a test piece 51 are integrally formed with thisthermostatic chamber. The test piece is transferred with a disk-shapedrotatable transfer turret 78 arranged between the upper anvil 52 and thelower anvil 53. A supply cylinder 79 for supplying the test piece isarranged above the transfer turret 78. Although not shown, a dischargeport for discharging a test piece that has undergone the test is formedin the rear portion of the thermostatic chamber 57. In this manner,transfer, supply, testing, and discharge of the sample are automatedunder the control of a computer. The arrangements and operations of therespective portions will be described.

(1) Sample Transfer Mechanism

FIG. 9 includes views showing the structure of the sample transferturret, in which FIG. 9(a) is a plane view, and FIG. 9(b) is a frontview. The transfer turret 78 is located at the central portion in thethermostatic chamber 57 and is directly coupled to a turret rotating aircylinder 80 provided on the external upper portion of the thermostaticchamber 57. The turret rotating air cylinder 80 rotates 45° per motion,and rotates intermittently under the control of pneumatic valves. Thetransfer turret 78 has eight test piece insertion holes to which clamps82 are attached respectively. The clamps 82 for fixing and holding thetest pieces 51 are normally closed with springs and opened uponoperation of clamp releases 83 provided at three predeterminedpositions. The clamp releases 83 are driven by clamp release aircylinders 84. The operating positions of the transfer turret 78 wherethe clamps 82 are opened/closed are fixed, which are three, i.e., asample supply position 86, a sample measurement position 87, and asample discharge position 88. A clamp release 83 and a clamp release aircylinder 84 are mounted for each of the three positions. The turretrotating air cylinder 80 and the clamp release air cylinders 84 areconnected to the computer to be controlled by it.

As the transfer turret 78 is arranged in the thermostatic chamber 57,the temperature in the thermostatic chamber 57 cannot be uniformedeasily. Thus, air is blown into the thermostatic chamber 57 to uniformthe temperature in it. An air circulation plate 85 is provided so thatair can circulate in the thermostatic chamber 57 easily. In this case,air is blown from a deep portion of the thermostatic chamber 57. The aircirculation plate 85 is provided obliquely on a corner side of sidewalls opposing the air-blowing portion, so that air is blown in thecirculating direction. Since air circulates in the thermostatic chamberin this manner, the temperature distribution in the thermostatic chamberis uniformed to decrease variations among test pieces. Although one aircirculation plate 85 is provided in FIG. 9, a plurality of aircirculation plates 85 can be provided.

The operation of the transfer turret under the control of the computerwill be described with reference to the flow chart of FIG. 10. In step91, a test piece 51 is supplied at the sample supply position 86. Thetest piece 51 fixed and held by the clamps 82 is transferred byclockwise rotation through 45° by one motion of the turret rotating aircylinder 80, and is stopped. After a lapse of 6 minutes in step 92, theflow advances to step 93, and whether six samples are supplied ischecked. If six samples have not been supplied, the flow advances tostep 94. The transfer turret rotates through 45°. Then, the flow returnsto step 91 to supply a sample. Sample measurement takes about 6 minutesand six samples are supplied to the sample measurement position 87,during which the samples are heated and lagged in the thermostaticchamber 57. The above described loop aims at equalizing the heating andlagging temperature so that all the samples are measured under the sameconditions. Accordingly, a sample requires 30 minutes to reach thesample measurement position 87, during which each sample is heated andlagged. Note that if a sample is measured within less than 6 minutes andheated and lagged for less than 30 minutes, this sample is additionallyheated and lagged at the measurement position.

When the test pieces 51 that are sequentially supplied and transferredreach the sample measurement position 87, the clamp releases 83 areactuated by the clamp release air cylinders 84 to open the clamps 82.Each test piece 51 is inserted between the upper and lower anvils 52 and53, and the test is started (step 95). During testing process, five testpieces 51 are present, from one at the sample supply position 86 to onewhich is before the sample measurement position 87 by one, as they arefixed and held by the transfer turret 78. During this process, thesetest pieces 51 are heated and lagged at a test temperature set in thethermostatic chamber 57. When the test is completed, the test piece 51is fixed and held by the clamp 82, and is transferred to the subsequentposition by rotation of the transfer turret 78 through 45° (step 96).The test piece 51 waits at this position until the subsequent test pieceis tested. When the test is completed, the test piece 51 is transferredto the sample discharge position 88. When the test piece 51 arrives atthis position, the clamp release air cylinder 84 is actuated to open theclamp 82, thereby discharging the test piece (step 97).

In step 98, whether all the samples have undergone measurement ischecked. If all the samples have not undergone measurement, the flowadvances to step 99 to check whether all the samples have been supplied.If all the samples have been supplied, the flow returns to step 95 toperform a measurement. If all the samples have not been supplied, moresamples are supplied in step 100, and the flow returns to step 95 toperform a measurement. In step 98, if all the samples have undergonemeasurement, the flow advances to step 101 to rotate the transfer turret78, thereby discharging the test pieces 51 remaining on the transferturret 78 (step 102).

(2) Sample Supply Mechanism

As shown in FIG. 8, the sample supply cylinder 79 is provided verticallyon the external upper portion of the thermostatic chamber 57, and asupply system is mounted on the vertical extension line of the samplesupply cylinder 79. FIG. 11 shows a schematic diagram of the samplesupply mechanism.

The test pieces 51 are inserted in the sample supply cylinder 79 fromthe upper side, so that 40 test pieces 51 are stacked in the samplesupply cylinder 79. The lowest test piece 51 is urged by a sample supplystopper 110 to be fixed on the inner wall of the sample supply cylinder79. The sample supply stopper 110 can be moved in the horizontaldirection by a sample supply stopper air cylinder 111. A sample platform112 is arranged below the vertical extension line of the sample supplycylinder 79, and can be vertically moved by a sample platform aircylinder 113. The sample platform 112 is normally set at the lowestportion of the downward movement of a piston 114. The sample supplystopper air cylinder 111 and the sample platform air cylinder 113 areconnected to the computer to be controlled by it.

The operation of this sample supply mechanism will be described.

When the transfer turret 78 rotates and stops at the sample supplyposition 86, the clamp release air cylinder 84 at the sample supplyposition 86 is actuated to operate the clamp release 83 at the samplesupply position 86, thereby opening the corresponding clamp 82.Subsequently, the sample platform air cylinder 113 is actuated to movethe sample platform 112 upward until it comes into contact with thelowest portion of the sample supply cylinder 79, so that the sampleplatform 112 waits for a test piece 51 to drop. Subsequently, the samplesupply stopper air cylinder 111 is actuated to separate the samplesupply stopper 110 from the test piece 51, and simultaneously all thetest pieces inserted in the sample supply cylinder 79 fall naturallyonto the sample platform 112. The sample supply stopper air cylinder 111is actuated so that the sample supply stopper 110 fixes the subsequenttest piece 51 by urging. Thereafter, the sample platform 112 is moveddownward, so that the circular cylindrical upper surface of the supplysample moves downward until it is level with the upper surface of thetransfer turret 78, and is stopped. Subsequently, the clamp release 83at the sample supply position 86 is actuated to close the correspondingclamp 82, thereby fixing and holding the test piece. This test sample istested by the sample measurement position 87, and waits for a subsequentoperation as it is held by the clamps 82 until the next instruction issupplied.

(3) Sample Test Mechanism

The test is started when the test piece 51 is transferred to themeasurement start position by the transfer turret 78. FIG. 12 shows thearrangement of this test mechanism. A ceramic member having an excellentheat insulating effect is inserted in the lower anvil 53 at the distalend portion of the piston side rod directly coupled to the piston rod ofthe hydraulic servo cylinder 55. The ceramic heat-insulating member ofthe lower anvil 53 is incorporated so that the temperature of heatbuild-up in the test piece is not conducted to the metal rod. On theupper side of the test piece, the upper anvil 52 is also integrallyformed with the load cell 54 side rod, and this rod is fixed to the loadcell 54 by screwing. The rod of the upper anvil 52 including the loadcell 54 has a hollow central portion, and the temperature sensor 61having a needle-like distal end is inserted in this hollow centralportion from above the test piece toward the central portion of the testpiece before the start of the test, in order to measure the temperatureof heat build-up in the test piece 51 during the test. The rods of theupper and lower anvils 52 and 53 have radiation fins 115 and 117,respectively, which are respectively cooled by air-cooling fans 116 and117 so that the heat will not be conducted to the piston side and loadcell side. A transverse vibration preventing mechanism fixed by aplate-shaped cross spring 119 is incorporated so that any transversevibration of the upper anvil 52 is prevented during the test.

The operation of the test mechanism will be described. When the testpiece 51 reaches the sample measurement position 87, the lower anvil 53moves upward and stops where the upper surface of the test piece 51comes into contact with the ceramic surface of the upper anvil 52. Theclamp 82 opens, and the test piece 51 stabilizes at the centers of theupper and lower anvils 52 and 53. The needle-like temperature sensorinserting mechanism is actuated to insert the needle-like temperaturesensor 61 to the central portion of the test piece 51 from above. Then,the test is started, and the lower anvil 53 moves upward until itapplies an initial load set by the computer to the test piece. Theinitial load applied to the test piece 51 is detected by the load cell54 and is fed back to the servo mechanism to control the upward movementof the lower anvil 53. In this fashion, the test piece 51 deforms by adegree corresponding to the initial load.

Regarding the mechanism for inserting the temperature sensor 61 into thetest piece 51, the computer is connected to the temperature sensorinserting servo motor 62 to control it. FIG. 13 includes views forexplaining the operation of the needle-like temperature sensor. As shownin FIG. 13(a), the distal end portion of the needle-like temperaturesensor 61 which is inserted into the test piece 51 at the start of thetest is inserted to a depth corresponding to the central portion of thetest piece 51. When an initial load is applied to the test piece todeform it, the temperature sensor 61 is controlled by the computer fromthe detection value of the differential transformer so that the depth ofits needle-like distal end portion is located at the center of thedeformed test piece 51. Thus, even if the fatigue of the test piece 51progresses and the test piece deforms largely, as shown in FIGS. 13(b)and 13(c), the needle-like temperature sensor 61 is controlled by theservo mechanism such that its distal end portion is constantly locatedat the center of the test piece 51, thus allowing accurate measurementof the temperature of heat build-up in the test piece 51.

When the temperature sensor 61 is inserted in the test piece 51, thelower anvil 53 applies a sinusoidal amplitude and frequency preset bythe computer to the test piece 51, thus starting the test. The vibrationis maintained until the test period preset by the computer ends. Whenthe test ends, the vibration of the lower anvil 53 is stopped. The testpiece 51 is held between the upper and lower anvils 52 and 53 in thedeformed state. In this state, the clamp release 83 at the samplemeasurement position 87 is actuated to close the corresponding clamp 82,thereby fixing and holding the test piece 51. Thereafter, the loweranvil 53 moves downward to a predetermined position and stops. When allthe operations of the test end, the transfer turret 78 rotates through45° to transfer the subsequent test piece 51 to a position between theupper and lower anvils 52 and 53 to wait for the subsequent test. Whenthe transfer turret 78 stops, the discharge operation of the test piece51 that has reached the sample discharge position 88 and the samplesupply operation progress simultaneously.

(4) Sample Discharge Mechanism

The test piece 51 that has undergone the test is fixed and held by theclamp 82, and is transferred to the sample discharge position 88 by thetransfer turret 78. FIG. 14 shows the structure of a sample dischargemechanism.

At the sample discharge position 88, a pusher air cylinder 120 and asample discharge port are incorporated in the thermostatic chamber 57 onthe extension line of the vertical line of the test piece 51. A sampledischarge port 121 extends to the outside of the thermostatic chamber57, and is always closed by a sample discharge port shutter 122, therebyshielding the heat in the thermostatic chamber 57 so that it will notleak to the outside.

When the test piece 51 that has undergone measurement is transferred tothe sample discharge position 88 and stops on the sample discharge port121, a shutter air cylinder 123 is actuated to open the sample dischargeport shutter 122. Subsequently, the clamp release air cylinder 84 at thesample discharge position 88 is actuated to open the clamp 82 with theclamp release 83 at the sample discharge position 88. The test piece 51that has undergone measurement falls through the sample discharge port121 to be discharged to the outside of the thermostatic chamber 57.

As the test piece 51 naturally falls through the sample discharge port121, it may sometimes be caught midway along the sample discharge port121 and cannot be discharged to the outside of the thermostatic chamber57. For this reason, the pusher air cylinder 120 is actuated to move apusher 124 at the distal end of the piston downward in the sampledischarge port to its lowest portion. Thereafter, the pusher 124 isreturned to the highest portion. When this operation ends, the sampledischarge port shutter 72 at the sample discharge position 88 is closedby the shutter air cylinder 123. The clamp release 83 is operated toclose the clamp 82, and waits for the subsequent movement.

In this manner, transfer, supply, testing, and discharge of the sampleare automated, so that the burden on the person in charge of measurementis decreased, thus allowing efficient measurement.

Possibility of Industrial Utilization

As has been described above, in the heat build-up/fatigue measuringmethod for a viscoelastic body and a hydraulic servo flexometeraccording to the present invention, since static and dynamic loads areapplied by using a hydraulic servo mechanism, highly precise follow-upcontrol and measurement can be performed, and test conditions close tothe actual conditions for use can be set. Thus, the present invention iseffective in prediction and detection of the heat build-upcharacteristics, occurrence of blow-out, and the like of viscoelasticbodies.

We claim:
 1. A heat build-up/fatigue measuring method which measuresheat build-up/fatigue of a viscoelastic body, in whicha strain and astress applied to a test piece are detected, static and dynamic loadsapplied to the test piece are controlled by a hydraulic servo mechanismbased on the detected strain and stress, a creep amount, a complexmodulus, and a loss tangent of the test piece are obtained based on thedetected strain and stress, and a time point at which blow-out willoccur is predicted based on changes over time of the creep amount, thecomplex modulus, the loss tangent, and the temperature of heat build-upof the test piece.
 2. A heat build-up/fatigue measuring method whichmeasures heat build-up/fatigue of a viscoelastic body, in whicha strainand a stress applied to a test piece are detected, static and dynamicloads applied to the test piece are controlled by a hydraulic servomechanism based on the detected strain and stress, a loss tangent of thetest piece is obtained based on the detected strain and stress, and arelationship between a minimum value of loss tangent and a time point atwhich blow-out occurs is obtained in advance, so that the time point atwhich blow-out occurs is obtained from the minimum value of the losstangent.
 3. A hydraulic servo flexometer for measuring heatbuild-up/fatigue of the viscoelastic body, comprising:an upper anvil anda lower anvil arranged in a thermostatic chamber to oppose each other tosandwich a viscoelastic test piece; a hydraulic servo mechanism formoving said upper anvil or said lower anvil in a vertical direction toapply static and dynamic loads to the test piece; hydraulic servocontrol means for controlling said hydraulic servo mechanism based on apreset test condition; a temperature detector for measuring atemperature of the test piece; a strain detector for detecting a strainapplied to the test piece; a stress detector for detecting a stressapplied to the test piece; a transfer turret which is arranged betweensaid upper anvil and said lower anvil, has an insertion hole formedtherein to insert a test piece therein, is provided with fixing meansfor holding and fixing the test piece inserted in the insertion hole,and rotates intermittently; a rotary driving unit for rotating saidtransfer unit; opening means for opening said fixing means, therebyreleasing the test piece; and a control unit for controlling saidhydraulic servo control means, said rotary driving unit, and saidopening means to fix the test piece at a supply position with fixingmeans, rotating said transfer turret until a test position and releasingthe test piece, fixing the test piece again with fixing means after thetest, and rotating said transfer turret until a discharge position andreleasing the test piece.
 4. The hydraulic servo flexometer according toclaim 3, further comprising:a sample supply cylinder arranged above thesample supply position of said transfer turret in a vertical directionand having a sample stopper in a lower side wall to be movable in atransverse direction; a vertically movable sample platform arrangedvertically below said sample supply cylinder; a stopper driving unit formoving said sample stopper in the transverse direction; a platformdriving unit for moving said sample platform in a vertical direction;and a control unit for controlling said stopper driving unit and saidplatform driving unit to load the sample on said sample platform whichhas moved upward to a lower end of said sample supply cylinder, andmoving said sample platform downward such that the sample is located ata position of said fixing means of said transfer turret.
 5. Thehydraulic servo flexometer according to claim 3, further comprising:asample discharge port provided vertically below the sample dischargeposition of said transfer turret; a sample discharge port shutterprovided at an inlet of said sample discharge port; a pusher movable ina vertical direction vertically above the sample discharge port; ashutter driving unit for moving said sample discharge port shutter; apusher driving unit for moving said pusher; and a control unit forcontrolling said shutter driving unit and said pusher driving unit toopen said shutter and to move said pusher downward only when dischargingthe test piece.
 6. A hydraulic servo flexometer for measuring heatbuild-up/fatigue of a viscoelastic test piece, comprising:an upper anviland a lower anvil arranged in a thermostatic chamber to oppose eachother to sandwich said viscoelastic test piece; a hydraulic servomechanism for moving said upper anvil or said lower anvil in a verticaldirection to apply static and dynamic loads to the test piece; hydraulicservo control means for controlling said hydraulic servo mechanism basedon a preset test condition; a temperature detector for measuring atemperature of the test piece; a strain detector for detecting a strainapplied to the test piece; and a stress detector for detecting a stressapplied to the tests piece; wherein said temperature detector comprisesa vertically movable temperature sensor having a pointed distal end,temperature sensor driving means for vertically moving said temperaturesensor, and a control unit which performs a control operation inaccordance with a detection value of said strain detector so that adistal end of said temperature sensor is located at a center of the testpiece.
 7. A hydraulic servo flexometer for measuring heatbuild-up/fatigue of a viscoelastic test piece, comprising:an upper anviland a lower anvil arranged in a thermostatic chamber to oppose eachother to sandwich a viscoelastic test piece; a hydraulic servo mechanismfor moving said upper anvil or said lower anvil in a vertical directionto apply static and dynamic loads to the test piece; hydraulic servocontrol means for controlling said hydraulic servo mechanism based on apreset test condition; a temperature detector for measuring atemperature of the test piece; a strain detector for detecting a strainapplied to the test piece; and a stress detector for detecting a stressapplied to the test piece; wherein said hydraulic servo flexometer isaccommodated and fixed in a hollow frame, and a vibration absorbingmember is packed in said frame.
 8. A hydraulic servo flexometer formeasuring heat build-up/fatigue of a viscoelastic test piece,comprising:an upper anvil and a lower anvil arranged in a thermostaticchamber to oppose each other to sandwich a viscoelastic test piece; ahydraulic servo mechanism for moving said upper anvil or said loweranvil in a vertical direction to apply static and dynamic loads to thetest piece; hydraulic servo control means for controlling said hydraulicservo mechanism based on a preset test condition; a temperature detectorfor measuring a temperature of the test piece; a strain detector fordetecting a strain applied to the test piece; a stress detector fordetecting a stress applied to the test piece; and an air circulationplate arranged on a surface opposing air blowing means of saidthermostatic chamber to circulate air along a side wall.